definition of plant harmones , inhibitors, retardants and their application on fruit canopy management with examples apple mango litchietc.

1. CANOPY MANAGEMENT THROUGH PLANT GROWTH
INHIBITORS:
Canopy Management: Canopy management is one of the most important
production factors confronting the burgeoning fruit industry in India. Indeed,
canopy management is the manipulation of tree canopy to optimize its
production potential with excellent quality fruits. In many fruit crops, increase
in production with enhanced fruit quality is obtained managing canopies of
short statured trees. Small trees capture and convert sunlight into fruit
production in a better way than larger ones. The main controlling factors are
amount of incoming radiations and percentage of radiations intercepted by tree
canopies.
Major principle: Maximum utilisation of light.
Plant Harmones Hormones are substances produced in very small amounts in
one part of the plant and transported to another part where they cause a
response. Plants produce a number of hormones that control various aspects of
growth, such as stem elongation; dormancy of buds and seeds; flowering; fruit
set, growth, and ripening; and the response to light and gravity.
Plant Growth Regulators: Plant growth regulators refer to an organic
compound other than nutrients and vitamins which are active at low
concentrations in promoting, inhibiting or modifying growth and development.
The naturally occurring (endogenous) growth substances are commonly known
as plant harmones, while the synthetic ones are called growth regulator.
1. Auxins (IAA, IBA, NAA, 2,4-D etc.)
2. Gibberllins (GA1, GA2, GA3 etc.)
3. Cytokinenins (Kinetin, Zeatin).
4. Ethylene (Ethrel)
5. Dormins (Abscissic acid, Phaseic acid).
6. Flowering Harmones (Florigen, Anthesin, Vernalin)
7. Phenolic substances (Coumarin)
8. Miscellaneous Natural Substances (Vitamins, Phytochrome tranmatic
Substances
Growth Retardants: The term growth retarding or growth retardant is that the
chemical slows cell division and cell elongation of shoot tissue and regulate
plant height physiologically without formative effects.

2. Eg. AMO 1618, Phosphin-D, CCC, MC and Alar, Malformis, Morphacting
Note: These do not occur naturally in plants and acts in retardation of stem
elongation, preventing cell division.
Growth Inhibitors:Suppress the growth of plants. There are phenolic inhibitors
and synthetic inhibitors and Abscissic acid (ABA). Benzoic acid, Salicylic acid,
Coumarin and Chlorogenic acid are examples for phenolic inhibitors, while
malichydrazide (MH) and Triiodo benzoic acid (TIBA) are examples of
synthetic inhibitors. Inhibitor from young leaves of Betula spp. prevents the
growth of apical buds eg. ABA and Dormin.
There are at least three basic mechanisms by which tree height can be restricted
by chemicals.
(a) By killing the terminal buds of branches or severely inhibiting apical
meristemic activity: The most important chemicals of this group include
Maleic Hydrazide (6-Hydroxy-3-(2H)-Pyidazione) and in some cases ethylene
and ethylene realising compounds. These chemicals, however, are not of much
use in controlling tree size in commercial fruit production as they also inhibit
normal leaf and flower initiation and development at the concentrations required
to be bring about growth inhibition of shoots.
(b) By reduced apical control: Reduction of tree height may also result from
simultaneous growth of many shoot axes, which owing to competition for
limited nutrients reduce the elongation of one or more axes on the same root
system. Promising chemicals for inducing auxiliary bud growth include TIBA
(2,3,5-Triiodobenzoic acid), which is an inhibitor of auxin synthesis and
translocation, cytokinins, particularly benzyl adenine, which promotes the
growth of auxiliary buds. Unlike those of the previous group, these chemicals
are not translocated to the meristem of the new lateral branches and hence do
not interfere with leaf and flower development.
(c) By inhibiting internodes elongation without disrupting apical
meristematic functions: Near specific inhibition of internodes elongation
without concomitant disruption of apical meristematic function and loss of
apical controls caused by certain growth retardants like, SADH (Succinic acid-
2, 2-dimethyl hydrazide), CCC, Amo-1618 and Paclobutrazol. These growth
retardants reduce gibberellins’s biosynthesis, though different retardants act at

3. different steps in biosynthesis pathway. Amo-1618 and SADH prevent the
conversion of trans-geranyl geranyl pyrophosphate to Kaurene and CCC blocks
Kaurenoic acid from getting converted to GA, whereas, Paclobutrazol retards
the formation of Kaurene-19-ol from Kaurene (Anon, 1984). The chemical
when applied to the leaves is readily translocated through phloem to the apical
meristem where it inhibit DNA synthesis resulting in a temporary check in
apical growth, thereby, promoting sprouting of auxiliary buds and reducing
intermodal elongation. Among tropical fruit trees, Cycocel at 6000 ppm inhibit
vegetative growth leading to reduction in plant height, intermodal length and
scion girth and promotion of flowering while CCC at 4000 ppm resulted in 50%
stunted growth in case of mango. More recently PP333 or Cultar has been found
more effective and persistent than these chemicals in tree size regulation.
1.Mango:
Mango responds well for growth retardant treatments. Among the several
chemicals, paculobutrazol has pronounced effect on flowering in mango.
Pruning the flowered/vegetative shoots 10 cm above the node during June-July
(immediately after harvest) followed by soil drenching with paculobutrazol 1
gm a.i per sq.m during August -September enhanced flowering, fruit set and
quality of fruit in Banganapalli mango under irrigated condition in the regular
season. Similarly, pruning 10 cm of terminal shoots after emergence of new
growth (floral or vegetative growth) during December–January followed by
application of paculobutrazol at 0.75 gm a.i. per tree of 9 year old during
March–April resulted in good off-season crop in cv Neelum. Here also, trees
subjected to this treatment should be under irrigation.
2. Guava:
Due to absence of dwarfing rootstocks in guava the pruning and use of growth
regulators play vital role in management of canopy. Paclobutrazol and
ethephon may be useful in high density planting as paclobutrazol helps in
making the plant dwarf by producing a retarding effect on the growth of tree
through inhibition of gibberellin biosynthesis, a key plant growth promoter.
Similarly, ethephon act as a ripening harmone and it enhances the ripening
process along with its growth retardation effect. Ethephon at higher
concenterations (500-3000ppm) proved to be quite effective in reducing the
plant height. The positive effect of PBZ application in restriction of vegetative
growth of guava plants. Stock and scion girth was found to be increased with

4. ethephon. The tree height and E-W tree spread was found to increase with
increasing plant density, PBZ 500ppm markedly restrict the plant growth.
2. Litchi:
Application of cultar (paclobutrazol) significantly reduced shoot growth as
compared to the control which resulted in profuse flowering, higher sex ratio,
increased fruit set and yield of ‘Rose Scented’ litchi. The TSS content of litchi
fruits was higher in cultar treated trees. Higher dose of cultar (5ml /m2 plant
spread) proved better than the lower dose of 3ml /m2 plant spread in controlling
vegetative flush and increasing flowering and yield. Similarly, cultar application
90days before bud break was found to be more effective than its application
60days before bud break. Paclobutrazol thus holds promise in increasing
flowering, fruits set, yield and quality of fruits.
3. Grapes :
Significant reduction in shoot length was observed with three sprays of Maleic
Hydrazide (MH 500 ppm at 5 leaf stage followed by 1000 ppm at leaf stage
and 1500 ppm at 15 leaf stage) when compared to control. Shoot length was not
significantly reduced by any of the 2- chloroethyl trimethyl ammonium chloride
(CCC) treatments. None of the treatments reduced the internodal length
measured between 5th and 6th ; 10th and 11th; and 15th and 16th nodes
significantly when compared to control. However application of CCC at 5 leaf
stage was more effective than other treatments in reducing the internodal length
between 5th and 6th; 10th and 11th; and between 15th and 16th nodes. Maleic
hydrazide (MH) seemed to be more effictive than CCC in increasing the cane
diameter in Thompson Seedless grape.
4. Apple :
Paclobutrazol and daminozide : Soil applications of paclobutrazol (PP333) had
no effect on vegetative growth of ‘Red Delicious’ apple, but both PP333 sprays
reduced shoot length. There was no significant difference between the single
and sequential paclobutrazol sprays. The growth of the daminozide treated
trees was not significantly different from that of those sequentially sprayed with
paclobutrazol (Jones et al., 1988). Sterrett (1985) studied the effect of
paclobutrazol injected into one-year old trees of ‘GoldenDelicious’ apple, to

5. evaluate growth inhibition response. The dose of 500µg of 14C-paclobutrazol
resulted in significant inhibition of shoot growth after 27days after injection.
5. Avacado :
The foliar sprays of paclobutrazol (PP333) and fruiting reduced the length of
the spring flush, with the former having the stronger dwarfing effect in both
cultivars of avacado. On average, fruiting and non-fruiting shoots were about
40- 42% shorter than controls after spraying
6. Strawberry :
Investigations carried out on strawberry with certain growth regulators revealed
that all the concentrations of both growth retardants viz. PP333 and cycocel
remarkably reduced crown height, leaf number and leaf area. However,
magnitude of inhibition was more at higher concentration. Maximum inhibition
of leaf area was 34 per cent in cycocel (1000ppm) treated plants as compared to
control.
7. Peach :
Dikegulac: Tree height and width decreased and lateral branching increased
with increasing concentration of dikegulac.
Paclobutrazol and ethephon : Cultivar ‘Crimson Gold’ nectarine trees (Prunus
Persica (L) Batsch) were treated with paclobutrazol (PP333) as a trunk drench
and fruits were thinned either by hand or by a spray with ethephon. No
Interactions between PP333 and ethephon were found .Vegetative growth was
reduced by PP333, both in terms of terminal shoot length and relative trunk
girth increment.
9.Cherry :
Daminozide and ethephon : In a study to determine possible effects of
combinations of ethephon and daminozide on growth, daminozide significantly
reduced average terminal growth at 2000 and 4000 ppm. Ethephon significantly
reduced growth only the first year of application (Facteau and Rowe, 1979).
Paclobutrazol : Jacyna et al. (1989) concluded that paclobutrazolsignificantly
decreased tree height, canopy diameter, mean shoot length and mean internode
length in ‘Bing’ sweet cherry in the year of application. The paclobutrazol +
Promalin gave a most promising result with the branching effect of Promalin

6. and the greater spur promotion of paclobutrazol. The internode-shortening
effect of paclobutrazol reduced the length of shoots with the combined
treatment, and it would be expected that these short shoots might also produce
many flowers.